This application is based on application No. 10-114766 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an image processor which removes background from image data.
2. Description of Prior Art
In the field of image data processing, it is known to divide digital image data into a plurality of areas, to decide the attribute of the image of each area and to compress image data according to the attribute. Digital image data are subjected to various processings such as edge emphasis.
In the image processing, background portions in image data may be discriminated and removed. In the background removal processing, it is known to detect the background by using a certain width (for example, between two values of average density) and to replace the portions decided to have background attribute with white background data.
However, the background removal has following problems. When background removal is performed on a photograph image, its highlight portions are liable to be removed. Further, it is desirable that the background is not removed for an image such as a photograph image having many highlight portions.
When the background is detected with a certain width, the resultant image may have discontinuous gradation at highlight density portions in correspondence to the threshold of the decision condition, and it may give artificial feeling for an image.
Further, in variable length coding, it is necessary to encode the white background efficiently in order to increase compression rate. Therefore, it is important to detect the background precisely.
An object of the present invention is to provide an image processor which can remove the background of an image without artificial feeling in a system for compressing image data.
In one aspect of the invention of an image processor, a background remover removes background from image data. A divider divides the image data, which have been subjected to the background removal, to a plurality of blocks, and an attribute discriminator means discriminates an attribute of image data in each block. A compressor compresses the image data in a block, from which the background has been removed, according to the attribute of the block.
In a second aspect of the invention of an image processor, a background remover removes an amount of background removal from image data, and an attribute discriminator means discriminates an attribute of the image data on which the background remover has removed a predetermined amount of the background. A controller changes the amount of background removal of the background remover according to the attribute. A compressor compresses the image data on which the background has been removed by the amount changed by the controller.
In a third aspect of the invention of an image processor, a background remover removes background from image data, and a first compressor compresses the image data which have been subjected to background removal. A divider divides the image data, which have been subjected to background removal, to a plurality of blocks, and an attribute discriminator means discriminates an attribute of image data in each block. Then, a second compressor compresses the image data in a block, which have been compressed, according to the attribute of the block.
An advantage of the present invention is that an image is recovered without artificial feeling at highlight portions thereof.
Another advantage of the present invention is that the amount of background remove can be set to a value appropriate to an image.
A further advantage of the present invention is that image quality is changed selectively according to the amount of background removal.